In X-ray photography applied in a medical field, etc., in general, an X-ray apparatus is used which adopts a rotating-anode X-ray tube assembly as an X-ray source. As the X-ray photography, Roentgen photography and computerized tomography (CT) are applied. The rotating-anode X-ray tube assembly comprises a housing, a rotating-anode X-ray tube provided in the housing to radiate X-rays, and a coolant (insulating oil) filled between the housing and the rotating-anode X-ray tube.
The housing is formed of a brittle material such as a cast aluminum. To an inner surface of the housing, a lead plate is provided to prohibit stray X-rays from emanating out of the housing. Also, at the housing, an X-ray transmission window is provided.
The rotating-anode X-ray tube comprises an anode target, a cathode and an envelope which accommodates the anode target and the cathode, and which is evacuated. The anode target can be rotated at a high speed (e.g., 10,000 RPM). The anode target includes a target layer (umbrella portion) formed of a tungsten alloy. The cathode is located eccentric from an axis of the anode target and opposite to the target layer.
Between the cathode and the anode target, a high voltage is applied. Thus, when being ejected from the cathode, electrons are accelerated and converted to collide with the target layer. As a result, the target layer emits X-rays, which transmit from the X-ray transmission window to the outside of the housing.
There is a case where an X-ray tube assembly for use in an X-ray CT scanner or a cardio-vascular imaging system is required to radiate X-rays having a high intensity. Also, there is a case where the X-ray tube assembly is required to continuously radiate X-rays for a long time or radiate X-rays with a high repetition rate. In this case, since it is necessary to forcibly cool a coolant, the X-ray tube assembly is provided with a cooler unit.
The cooler unit is provided at part of a circulation path for the coolant, and is located outside the housing. The cooler unit comprises a heat exchanger, a conduit which is connected to the housing and the heat exchanger to form the circulation path for the coolant, and a circulation pump which circulates the coolant in the circulation path. In accordance with how heat transmitted from the coolant to the heat exchanger is dissipated, the cooler unit is broadly classified into an air-cooling type of cooler unit and a water-cooling type of cooler unit. The air-cooling type of cooler unit forcedly cools the heat transmitted from the coolant to the heat exchanger using forced air flow. The water-cooling type of cooler unit transmits the heat transmitted from the coolant to the heat exchanger to a water-based coolant having a lower temperature than the above former coolant. In this case, in order to dissipate the heat transmitted to the water-based coolant, an air-cooling type of cooler unit is provided in a circulation path for the water-based coolant.